Brown-Out Detection - Philips LPC213 Series User Manual

Philips Semiconductors
Volume 1
Any of the various Resets can bring the microcontroller out of power-down mode, as can
the external interrupts EINT3:0, plus the RTC interrupt if the RTC is operating from its own
oscillator on the RTCX1-2 pins. When one of these interrupts is enabled for wakeup and
its selected event occurs, an oscillator wakeup cycle is started. The actual interrupt (if any)
occurs after the wakeup timer expires, and is handled by the Vectored Interrupt Controller.
However, the pin multiplexing on the LPC2131/2/4/6/8 (see chapters "Pin Configuration"
on page 64 and "Pin Connect Block" on page 73) was designed to allow other peripherals
to, in effect, bring the device out of Power-down mode. The following pin-function pairings
allow interrupts from events relating to UART0 or 1, SPI 0 or 1, or the I
SDA / EINT1, SSEL0 / EINT2, RxD1 / EINT3, DCD1 / EINT1, RI1 / EINT2, SSEL1 /
EINT3.
To put the device in Power-down mode and allow activity on one or more of these buses or
lines to power it back up, software should reprogram the pin function to External Interrupt,
select the appropriate mode and polarity for the Interrupt, and then select Power-down
mode. Upon wakeup software should restore the pin multiplexing to the peripheral
function.
All of the bus- or line-activity indications in the list above happen to be low-active. If
software wants the device to come out of power -down mode in response to activity on
more than one pin that share the same EINTi channel, it should program low-level
sensitivity for that channel, because only in level mode will the channel logically OR the
signals to wake the device.
The only flaw in this scheme is that the time to restart the oscillator prevents the
LPC2131/2/4/6/8 from capturing the bus or line activity that wakes it up. Idle mode is more
appropriate than power-down mode for devices that must capture and respond to external
activity in a timely manner.
To summarize: on the LPC2131/2/4/6/8, the Wakeup Timer enforces a minimum reset
duration based on the crystal oscillator, and is activated whenever there is a wakeup from
Power-down mode or any type of Reset.

3.12 Brown-out detection

The LPC2131/2/4/6/8 includes 2-stage monitoring of the voltage on the V
voltage falls below 2.9 V, the Brown-Out Detector (BOD) asserts an interrupt signal to the
Vectored Interrupt Controller. This signal can be enabled for interrupt in the Interrupt
Enable register (see
0xFFFF F010)" on page
Interrupt Status register (see
0xFFFF F008)" on page
The second stage of low-voltage detection asserts Reset to inactivate the
LPC2131/2/4/6/8 when the voltage on the V
alteration of the Flash as operation of the various elements of the chip would otherwise
become unreliable due to low voltage. The BOD circuit maintains this reset down below
1 V, at which point the Power-On Reset circuitry maintains the overall Reset.
Both the 2.9 V and 2.6 V thresholds include some hysteresis. In normal operation, this
hysteresis allows the 2.9 V detection to reliably interrupt, or a regularly-executed event
loop to sense the condition.
User manual
Section 5.4.4 "Interrupt Enable register (VICIntEnable -
52); if not, software can monitor the signal by reading the Raw
Section 5.4.3 "Raw Interrupt status register (VICRawIntr -
52).
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Rev. 01 — 24 June 2005
UM10120
Chapter 3: System Control Block
pins falls below 2.6 V. This Reset prevents
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
2
C: RxD0 / EINT0,
pins. If this
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